Rock core drill bit

ABSTRACT

A core drill bit ( 1 ) for working brittle material has an axially extending tubular shaft ( 2 ) with a rotation driver ( 4 ) coaxially fitted to a trailing end portion ( 3   a ) and a plurality of had material inserts ( 5   a,    5   b ) arranged on the opposite open leading end portion ( 3   b ), which are formed with a defined cutting edge, whereby each individual hard material insert ( 5   a,    5   b ) is fitted on precisely one intermediate carrier members ( 6   a,    6   b ) associated therewith, which is fitted on the leading open end portion ( 3   b ) of the tubular shaft ( 2 ).

BACKGROUND OF THE INVENTION

[0001] The invention relates to a core drill bit for working brittle materials such as rock, concrete and masonry.

[0002] This type of core drill bit with diameters of several 100 mm are comprised of a tubular shaft with a rotation driver that is coaxially attached at the trailing end portion for coupling with a rotational tool device and a plurality of inserts formed of hard material fixedly arranged, by hard soldering, at the open or leading end portion, which are, configured, for example, without defined cutting edges but as sintered diamond coating.

[0003] According to DE3407427 at least three hard material inserts with a defined cutting edge are configured as PCD cutting elements (hard material insert with polycrystalline synthetic diamond coating) and configured with a negative cutting angle and rounded edges. The open leading end portion has the inserts of hard material inserted directly into axial recesses and is formed as a part, subject to wear, in the form of a modular, prefabricated crown ring made of high-grade steel, which is soldered to the tubular shaft.

[0004] According to DE424465, a core drill comprises three differently arranged and shaped PCD cutting elements which are fitted directly in axial recesses of the tubular shaft. For the direct fitting of the hard material inserts by hard soldering or electron beam welding, the recesses of the tube must be formed with a high surface quality in the fitting zone of the hard material inserts, which is particularly technologically costly especially because of the variety of core bits of varying diameters.

SUMMARY OF THE INVENTION

[0005] The object of the invention is to provide a core drill bit with defined cutting edges that is economical to manufacture.

[0006] Essentially a core bit comprises an axially extending tubular shaft with a coaxially fitted rotation driver at its trailing end portion for coupling with a rotational tool device and a plurality of inserts made of hard material are arranged at the leading end, which are provided with a defined cutting edge, whereby each individual hard material insert is fitted to an intermediate carrier member, which is fitted on the open leading end portion.

[0007] Since only the intermediate carrier member made of metal, high-quality metal casting or sintered metal must be formed with high surface quality in the fitting zone of the hard material inserts, modular pre-fabrication of the intermediate carrier member including the fitting of the hard material inserts is possible, which is always uniform and thus technically easy.

[0008] The intermediate carrier members are manufactured advantageously of plastically deformable metal such as high-quality steel, whereby the intermediate carrier members can be bent only after fitting of the hard material inserts corresponding to the diameter of the core drill crown and thus the variety of intermediate carrier members of different diameters is technologically easier to manufacture.

[0009] Advantageously, two or three different groups of intermediate carrier members are available, which differ in the axial and radial arrangement of the hard material inserts, whereby locally higher point contact forces using the same hard material inserts can be achieved.

[0010] The plurality of intermediate carrier members is advantageously fitted on a completely flat end surface of the tubular shaft, which is easily manufactured.

[0011] The side of the intermediate carrier member receiving the hard material insert is partially concave in form in order to conduct the forces from the hard material insert without appreciable local excess stress in the tubular shaft.

[0012] Advantageously, the axial height of the intermediate carrier member decreases opposite the direction of rotation, whereby an increasing clearance is formed behind the hard material insert.

[0013] Preferably, the thickness of the intermediate carrier member corresponds substantially to the thickness of the hard material insert, whereby the later is fitted as to be resistant to breakage.

[0014] The intermediate carrier members are advantageously thicker than the wall thickness of the tubular shaft, whereby a sufficiently stable fitting of the hard material insert is possible even in the case of a thin-walled tubular shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention will be more completely described with reference to the following figures, wherein:

[0016]FIG. 1 is an axially extending perspective view of a core drill bit partially cut away;

[0017]FIG. 2 is a schematic leading end view of a core drill bit having four cutting segments;

[0018]FIG. 3 is a schematic leading end view of a core drill bit having five cutting segments; and

[0019]FIG. 4 is a schematic leading end view of a core drill bit having two cutting segments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] According to FIG. 1, a core drill bit 1 shown partly in longitudinal section has an axially extending tubular shaft 2 with a coaxially fitted rotation driver 4 at its trailing end portion 3 a and a plurality of hard material inserts 5 a, 5 b, formed as PCD cutting elements, arranged on the opposite open leading end 3 b. Each individual hard material insert 5 a, 5 b is fitted to a separate intermediate carrier members 6 a, 6 b, which is secured to the leading end portion 3 b. The hard material insert 5 a of the intermediate carrier member 6 ais radially and axially easily displaced toward the hard material insert 5 b of the intermediate carrier member 6 b, whereby two different groups of intermediate carrier members 6 a, 6 b are available. All intermediate carrier members 6 a, 6 b are fitted on a completely flat leading end surface 2 a of the tubular shaft 2. A side 7 of the intermediate carrier members 6 a, 6 b receiving the hard material insert 5 a, 5 b is formed partially concave. The axial height H of the intermediate carrier members 6 a, 6 b varies, as shown in FIG. 1, and corresponds substantially to, or is slightly smaller than, the width B of the hard material insert 5 a, 5 b. The radial width or wall thickness W is greater than the radial wall thickness of the tubular shaft 2. The thickness D of the intermediate carrier members 6 a, 6 b decreases in the direction opposite to the direction of rotation R.

[0021] According to FIGS. 2, 3 and 4, a variety of core drill bits 1 of different diameters are formed with a plurality of uniform groups of intermediate carrier members 6 a, 6 b. 

What is claimed is:
 1. A core drill bit for working brittle materials such as rock, concrete and masonry comprises an axially extending tubular shaft (2) having an open leading end (3 b) and a trailing end (3 a), a coaxial rotation driver secured to the trailing end (3 a) of said tubular shaft (2) and a plurality of hard material inserts (5 a, 5 b) arranged on the leading end thereof, said hard material inserts having a defined cutting edge, each of said hard material inserts (5 a, 5 b) is fitted on a separate intermediate carrier members (6 a, 6 b) associated therewith, and said intermediate carrier members are fitted to the leading end (3 b) of said tubular shaft.
 2. A core drill bit, as set forth in claim 1, wherein said intermediate carrier members (6 a, 6 b) are formed of a plastically deformable metal.
 3. A core drill bit, as set in claim 1, wherein at least two different said intermediate carrier members are secured to said tubular shaft being different in the axial and radial arrangement of said hard materials inserts (5 a, 5 b).
 4. A core drill bit, as set forth in claim 1, wherein the plurality of said intermediate carrier members (6 a, 6 b) are secured to a completely flat leading end face (2 a) of said tubular shaft.
 5. A core drill bit, as set forth in claim 1, wherein a side (7) of said intermediate carrier members (6 a, 6 b) mounting said hard material inserts (5 a, 5 b) is partially concave extending in a rotation direction (R).
 6. A core drill bit, as set forth in claim 1, wherein at least one of an axial height (H) and a radial thickness (D) of said intermediate carrier members (6 a, 6 b) decrease in a direction opposite to a direction of rotation (R) of said core drill bit.
 7. A core drill bit, as set forth in claim 6, wherein the radial thickness (D) of said intermediate carrier members (6 a, 6 b) corresponds substantially to a radial width (B) of the corresponding said hard material inserts (5 a, 5 b).
 8. A core drill bit, as set forth in claim 1, wherein said intermediate carrier members (6 a, 6 b) are thicker in the radial direction than a radial wall thickness (W) of said tubular shaft to which said intermediate carrier members (6 a, 6 b) are secured. 